The spinal column, which is the central support to the vertebrate skeleton and a protective enclosure for the spinal cord, is a linear series of bones, or vertebrae. Inter-vertebral discs separate and reduce friction between adjacent vertebrae and absorb compression forces applied to the spinal column. Spinal nerves that extend from each side of the spinal cord exit the column at inter-vertebral forama.
A typical vertebra comprises an anterior body, and a posterior arch that surrounds the spinal cord lying within the vertebral foramen formed by the arch. The muscles that flex the spine are attached to three processes extending from the posterior arch. On the upper surface of each vertebra in a standing human are two superior articulated processes that oppose two inferior articulated processes extending from the lower surface of an adjacent vertebra. Facets on the opposing processes determine the range and direction of movement between adjacent vertebrae, and hence the flexibility of the spinal column.
Back pain is one of the most significant problems facing the workforce in the United States today, is a leading cause of sickness-related absenteeism, and a major cause of disability for people between the ages of 19 and 45. Back pain can occur from pinching or irritating a spinal nerve, compression of the spine, vertebral shifting relative to the spinal cord axis, and formation of bone spurs. The most common cause of disabling back pain, however, generally stems from trauma to a vertebral disc, such as from mechanical shock, stress, tumors, or degenerative diseases. In many cases, the disc can become permanently damaged or degenerated, such that the preferred treatment necessitates partial or total excision and replacement of the damaged disc.
Traumatic injury to a vertebral disc that is not removed frequently can promote scar tissue formation. Such scar tissue typically is thicker than the healthy tissue, such that the disc continues to progressively degenerate, lose water content, and can stiffen and become significantly less effective as a shock absorber. Eventually, the disc can deform, herniate, or collapse, eliminating the flexibility of the spinal column, and potentially leading to further degeneration or damage to other vertebral discs of the spinal column. At such a point, the only option is for the damaged disc to be partially or completely removed. When the disc is partially or completely removed, generally it is necessary to replace the excised material to prevent direct contact between the boney surfaces of the adjacent vertebrate on either side of the removed disc. For example, a vertebral spacer is inserted between adjacent vertebrate to provide restorative force and function as a shock absorber between the adjacent vertebrate. Another alternative approach has been to insert a “cage” that can maintain a space occupied by the removed disc to prevent the vertebrate from collapsing and impinging upon the nerve roots of the spine. Still further, spinal fusion has been used to restrict motion and stabilize patients' spines by fusing adjacent vertebrate together. This generally can reduce mechanical back pain by preventing the now immobile vertebrate from impinging on a spinal nerve; however, such stability and pain reduction generally is created at the expense of spinal flexibility and motion.
Thus, many conventional techniques for disc repair and replacement can be limited in terms of their size or configuration of the implant and thus generally are not designed to accommodate variations in size of the gap resulting from the excising of the vertebral disc material. However, conventional techniques often require installation of an implant through the patients front side, or anterior, or require a larger surgical opening be placed in the patients back to introduce a traditional rod and pedicle screw system. Installation of the traditional systems may require the dissection of muscles, undergoing a surgical procedure lasting long in duration, extensive blood loss during surgery, increased risk of nerve damager to the patient and oftentimes increasing the patient's recovery time.